The act of searching out somebody who has just achieved something good and then instantly ruining it for them by doing something annoying to take the shine off of it. Usually a whole day activity as finding somebody who has just achieved success isn't easy.

If someone gets a good grade in an exam, throw a pint of milk in their face.

If a kid learns to ride a bike for the first time, run up and push it over.

The Urban Dictionary T-Shirt

can be used to describe an object or person that has angered or "pissed" you off

oh you bastarding twat, can't you even get it bastarding right you fucking bastarding arsehole, get that bastarding thing which cant stay in its bastarding place for one bastarding minute and fucking pass it over bastarding here... etc etc